FIG. 2 is a sectional view of a conventional disk recorder or player apparatus. A disk 60, which is a magneto-optical disk, is rotatably housed in a cartridge 6 having openings formed in upper and lower faces thereof. A turn table 70 and a pickup 7 movable toward and away from the turn table 70 are provided on a chassis 1 which receives the cartridge 6. A recording head 72 is attached to the pickup 7 via a head lever 71. A portion of the disk 60 is irradiated with a beam from the pickup 7 thereby to be heated at a Curie temperature and, at the same time, an upper surface portion of the disk 60 is magnetized by the recording head 72 for recording a signal therein. In signal reproduction, the disk is irradiated with a beam from the pickup 7, and the level (0-level or 1-level) of a recorded signal is determined on the basis of the diffractive direction of a light beam reflected on the disk.
The chassis 1 and the cartridge 6 are housed in a cabinet 2 constituted by cabinet halves 20, 21 which are vertically combined together. A circuit board 3 for energization of the pickup 7 and the turn table 70 is provided in the lower cabinet half 21. The circuit board 3 is composed of a glass epoxy resin or the like. It is noted that the position of the circuit board 3 is not limited to that shown in FIG. 2.
Since circuit components (not shown) mounted on the circuit board 3 generate heat during the signal recording and reproduction, the internal temperature of the cabinet 2 is liable to rise. In view of the rise of the internal temperature of the apparatus, the applicant of the present invention intends to guarantee that the apparatus normally operates at a temperature up to 70° C., and checks the apparatus to confirm that the apparatus does not malfunction at a temperature of 70° C. or lower when the apparatus is mass-produced.
The applicant found that the apparatus suffered from the following problem.
The applicant found that, when the apparatus was left at a high temperature, the surface of the disk 60 was fogged so that the C/N ratio of the reproduced signal was reduced or the disk 60 was not accurately magnetized in the recording. The applicant analyzed a substance deposited on the surface of the disk 60, and found that the major component of the substance was ammonium sulfate (NH4)2SO4. However, none of the components provided in the apparatus were produced by employing ammonium sulfate, and there was no evidence that ammonium sulfate externally adhered onto the disk.
The applicant investigated the mechanism of the generation of ammonium sulfate and, as a result, found that ammonium sulfate was generated by the following chemical reactions.
As described above, the circuit board 3 is composed of the glass epoxy resin. Further, cases of the mounted circuit components are often composed of an epoxy resin. As well known, the epoxy resin is synthesized from bisphenol-A having a molecular formula (CH3)2C(C6H4OH)2 and epichlorohydrin C3H5OCl.
Therefore, if the epoxy resin is left at a high temperature for a long period of time, bisphenol-A is decomposed and modified to undergo condensation polymerization, so that some of functional groups are removed from bisphenol-A. As a result, water and ammonia are generated as by-products. Ammonia NH3 is present in the form of molecules in a trace amount, but reacts with sulfur dioxide gas present in the atmosphere to provide ammonium sulfate (NH4)2SO4 as follows:SO2+H2O+O→H2SO4H2SO4+2NH3→(NH4)2SO4
That is, the applicant found that, where the circuit board 3 was left at around the operation guarantee temperature (70° C.) for a long period of time, ammonia is generated and, as a result, the disk 60 was fogged. With a recent trend toward the size reduction and thickness reduction of the apparatus, the cabinet 2 has a higher internal temperature. Therefore, an ammonia concentration in the cabinet 2 tends to be increased, making the disk more liable to be fogged.
It is an object of the present invention to prevent the fogging of the disk even if the disk is left at a high temperature in the apparatus for a long period of time.